The beta-cell mass is determined by the balance between the rates of beta-cell death (apoptosis) and the birth of new beta-cells (neogenesis). In the rat and mouse pancreas the beta-cell mass turns over approximately every 30 days (2-3%/day) due to apoptosis and the formation of new beta-cells as they differentiate from progenitor cells located in the pancreatic ducts. The applicant proposes a "transcription factor hypothesis" as a cause of diabetes. This hypothesis states that specific transcriptional proteins, that regulate the expression of specific genes during pancreas development, are responsible for beta-cell neogenesis and apoptosis and that malfunctioning of these proteins may curtail beta-cell growth and function. The applicant has identified two such proteins involved in neogenesis: the homeodomain protein IDX-1 and the Pou-homeodomain protein Brain4 as key regulators of beta-cell and alpha-cell development, respectively. The intestinal incretin hormone glucagon-like peptide appears to stimulate the expression of IDX-1 and the neogenesis of beta-cells. We have also identified two bZIP (leucine zipper) proteins, C/EBPbeta and CHOP, that appear to participate in the apoptosis of beta-cells in cell culture models in vitro and by genetic manipulations of mice in vivo. The applicant believes that a fundamental understanding of how the expression of IDX-1, Brn4, C/EBPbeta and CHOP are regulated during pancreas development, islet cell neogenesis and apoptosis will provide opportunities for the development of future therapeutic approaches for the cure of diabetes.